Someone picked up the development, go >here< to follow the progress and send your issues
Here is my multi converter, it can convert m2, wmo, adt, wdt and anim (7.3.5) from Legion to be used on wotlk (map can be visited with the client or edited with noggit).
M2 using .skel are not supported.
To use it just open it then drag and drop the files you want to convert (or a folder containing some, subfolder included) and click on "Fix", the files will be overwritten and it will delete the files that are unused on wotlk. If the .skin files are in the same folder they will be converted too.
M2 already converted to LK format won't be converted again. As for WMO converting them multiple time won't affect them.
ADT need their _tex0 and _obj0 counterpart to be converted.
Warning: don't take the WDL files from blizzard, they have changed and causes wow error.
Warning 2: the next releases of Noggit will require you to use the version 3.3 or newer, the m2 converted with the old versions were missing some data that Noggit now need, without it'll crash.
What needs to be done :
- Fix forward flying animation for a few models
- Animation particles
- Set WMOs liquid types that correspond when the ID is too high
- Set fel liquid to green lava on adt for a better / more accurate look
Some map might not look good because several effect like texture scaling that aren't there in wotlk, the 2 additional layers for texture introduced in wod, ...
For those who want to report a problem :
Tell me on which model(s) you've seen the problem and add screen(s), it help me fixing the problem faster. And send me your error.log where there are errors during the conversion !!
And please use an external website to upload the screens because each time I upload a new version the screenshots in comments appear in the changelog for some reasons and I have to delete them which also delete them from the comments 
Thanks a lot to :
- All those who contributed / are contributing to the wiki, I couldn't have done it without this precious source of informations!
- Mjollna for her m2 converter and awesome ADT diagram!
- PhillipTNG for his m2 conversion script which helped me write mine in the beginning.
Sources are now available, see last release.
